Download “Mastodon” from an app store. Create an account. Post.
It’s been a few years since you last tried, right?
It offers you a server, which is a step up, but the option to pick a different one is still very prominent which is going to make some people ask questions and lead to the usual confusion and anxiety about picking the “right” one.
Anyone who has studied UX and how users move through an app knows that every step you make someone do has a huge drop off in user completion of that process.
Unfortunately that means that centralized, simple platforms will always have a distinct UX advantage over federated platforms. We have to make up for it by being simply better. (No ads is a good start.)